1. Field of the Invention
The present invention relates to a sensor arrangement for image recognition, having a plurality of optical sensor elements arranged in a raster layout and responding to light in the visible wavelength range.
2. Description of the Prior Art
It is known that a digital camera can be arranged in a motor vehicle in order to photograph an image of the driver, wherein the image of the driver photographed by the camera can be analyzed in different ways.
One possible technical application comprises connecting the camera to a video telephone in order to allow a video telephone transmission from the motor vehicle.
A further technical application comprises a fatigue detection system in which images of the driver's face are photographed during the journey, the fatigue state of the driver being derived from the frequency of blinking, for example.
Finally, the image of the driver photographed by the camera can also be used to identify the driver, in order to permit the use of the motor vehicle only by a specific person with a predetermined physiognomy, while disabling the motor vehicle for other people.
A problem arises in this context, in that precisely defined light conditions must be present for both the fatigue detection and the person identification, in order to prevent an erroneous identification due to fluctuating light conditions. Therefore, for the purpose of fatigue detection and person identification, the use of an infrared camera is known, so that exactly defined lighting conditions can be created by means of infrared spotlights.
However, this has the disadvantage that, in addition to the daylight-sensitive camera for the video telephone, an infrared camera is required for the fatigue detection and the person identification.
EP 0 605 259 A2 discloses an optical sensor arrangement as a component of a copying device, which arrangement has both sensor elements for visible light and sensor elements for infrared light. In this context, however, a halogen lamp is used to provide broadband lighting of the photograph object, the halogen lamp triggering both the sensor elements for visible light and the sensor elements for infrared light. Therefore the known sensor arrangement requires optical filters for image separation.